Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “space group”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Broadband light emitting zero-dimensional antimony and bismuth-based hybrid halides with diverse structures

Low-dimensional organic–inorganic metal halides have recently attracted extensive attention because of their various structures and distinguished photoelectric properties. Herein, we report a series of new zero-dimensional organic–inorganic hybrid metal halides: (TMEDA) 3 Bi 2 Cl 12 ·H 2 O, (TMEDA) 3 Bi 2 Br 12 ·H 2 O, (TMEDA) 3 Sb 2 Br 12 ·H 2 O, and (TMEDA) 5 Sb 6 Cl 28 ·2H 2 O [TMEDA = N,N,N'·trimethylethylenediamine]. (TMEDA) 3 M 2 X 12 ·H 2 O (M = Bi or Sb, X = Cl or Br) crystallizes in the monoclinic space group P2 1 /n, and (TMEDA) 5 Sb 6 Cl 28 ·2H 2 O crystallizes in the orthorhombic space group Pnma. (TMEDA) 3 M 2 X 12 possesses a zero-dimensional structure with the metal halide ions of [MBr 6 ] 3- isolated by the organic TMEDA 2+ cations. Interestingly, the (TMEDA) 5 Sb 6 Cl 28 ·2H 2 O structure consists of a combination of corner-connected octahedra [Sb 4 Cl 18 ] 6- and edge-shared [Sb 2 Cl 10 ] 4- , which is quite rare. The light emission of all these compounds was measured, and (TMEDA) 3 Sb 2 Br 12 ·H 2 O exhibits the most intense luminescence. Upon 400 nm ultraviolet light excitation, (TMEDA) 3 Sb 2 Br 12 ·H 2 O exhibited strong broadband yellow emission centered at 625 nm with a full-width at half-maximum of ~150 nm originating from self-trapped excitons. In conclusion, this work suggests the possibility of new types of hybrid halides by introducing different metal centers and probing the structural evolution and photoluminescent properties, serving as a reference for the relationship between structure and luminescent performance and demonstrating their potential use as phosphors in light-emitting diodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Cation reordering instead of phase transitions: Origins and implications of contrasting lithiation mechanisms in 1D ζ- and 2D α-V 2 O 5

Substantial improvements in cycle life, rate performance, accessible voltage, and reversible capacity are required to realize the promise of Li-ion batteries in full measure. Here, we have examined insertion electrodes of the same composition (V 2 O 5 ) prepared according to the same electrode specifications and comprising particles with similar dimensions and geometries that differ only in terms of their atomic connectivity and crystal structure, specifically two-dimensional (2D) layered α-V 2 O 5 that crystallizes in an orthorhombic space group and one-dimensional (1D) tunnel-structured ζ-V 2 O 5 crystallized in a monoclinic space group. By using particles of similar dimensions, we have disentangled the role of specific structural motifs and atomistic diffusion pathways in affecting electrochemical performance by mapping the dynamical evolution of lithiation-induced structural modifications using ex situ scanning transmission X-ray microscopy, operando synchrotron X-ray diffraction measurements, and phase-field modeling. We find the operation of sharply divergent mechanisms to accommodate increasing concentrations of Li-ions: a series of distortive phase transformations that result in puckering and expansion of interlayer spacing in layered α-V 2 O 5 , as compared with cation reordering along interstitial sites in tunnel-structured ζ-V 2 O 5 . By alleviating distortive phase transformations, the ζ-V 2 O 5 cathode shows reduced voltage hysteresis, increased Li-ion diffusivity, alleviation of stress gradients, and improved capacity retention. The findings demonstrate that alternative lithiation mechanisms can be accessed in metastable compounds by dint of their reconfigured atomic connectivity and can unlock substantially improved electrochemical performance not accessible in the thermodynamically stable phase.

25 ENERGY STORAGE↗
DOE OSTI2023

Luminescence of alkali rare earth borates A 3 Ln(BO 3 ) 2 (A = Na, K; Ln = Eu, Tb)

Single crystals of a series of rare earth borates, A 3 Ln (BO 3 ) (A = Na, K; Ln = Eu, Tb), were synthesized using a boric acid/hydroxide melt. The Na 3 Ln (BO 3 ) 2 borates crystallized in the monoclinic system with space group P2 1 /n, and the K 3 Ln (BO 3 ) 2 borates crystallized in the orthorhombic system with space group Pnma. Here, the luminescence of these borates was investigated under ultraviolet and X-ray excitations for the first time. Radioluminescence (RL) measurements showed K 3 Tb(BO 3 ) 2 to be the brightest compound, with an integral intensity equal to 55% of the integral emission of Bi 4 Ge 3 O 12 (BGO) powder.

36 MATERIALS SCIENCE↗
DOE OSTI2022

High-pressure phase transitions and melt structure of Pb O 2 : An analog for silica

In situ x-ray diffraction measurements and inverse Monte Carlo simulations of pair distribution functions were used to study the structural response of PbO 2 under pressure and to characterize the local structure of liquid PbO 2 . Two phase transitions are observed upon room-temperature compression of crystalline PbO 2 up to ~65 GPa. Here, the starting mixture of rutile structured β– PbO 2 and orthorhombic α– PbO 2 undergoes a transition to a ZrO 2 -type orthorhombic phase with space group Pbca at ~21 GPa. Above 42 GPa, the Pbca phase transforms to a cotunnite-type phase with space group Pnam. In this paper, we also report short-range order in liquid PbO 2 , showing ~8–9-fold and 4–5-fold coordination around Pb and O atoms, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Symmetric U(1) and Z 2 spin liquids on the pyrochlore lattice

The geometrically frustrated three-dimensional pyrochlore lattice has been long predicted to host a quantum spin liquid, an intrinsic long-range entangled state with fractionalized excitations. To date, most proposals for pyrochlore materials have focused on quantum spin ice, a U(1) quantum spin liquid whose only low energy excitations are emergent photons of Maxwell type. Here, we explore the possibility of finding pyrochlore quantum spin liquids whose low energy theories go beyond this standard one. We give a complete classification of symmetric U ( 1 ) and Z 2 spin liquids on the pyrochlore lattice within the projective symmetry group framework for fermionic spinons. We find 18 U ( 1 ) spin liquids and 28 Z 2 spin liquids that preserve pyrochlore space-group symmetry while, upon further imposing time-reversal symmetry, the numbers of classes become 16 and 48, respectively. For each class, the most general symmetry-allowed spinon mean-field Hamiltonian is given. Interestingly, we find that several U(1) spin liquid classes possess an unusual gapless multi-nodal-line structure (“nodal star”) in the spinon bands, which is protected by the projective actions of the threefold rotation and screw symmetries of the pyrochlore space group. Through a simple model, we study the effect of gauge fluctuations on such a nodal star spin liquid and propose that the leading terms in the low temperature specific heat have the scaling form C / T ~ T + T / ln T , in contrast to the form C / T ~ T 2 of the standard U(1) pyrochlore spin liquid with gapped spinons.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Eu 5 Al 3 Sb 6 : Al 4 Tetrahedra Embedded in a Rock-Salt-Like Structure

The new Eu 5 Al 3 Sb 6 phase has been successfully synthesized as a pure phase through Sn flux methods yielding large, high-quality crystals. This structure type features disordered Al clusters that appear in the form of dual tetrahedra. It crystallizes in the monoclinic C2/m space group exhibiting a rock-salt-like Eu–Sb framework with [Al 4 ] tetrahedra replacing some of the cationic Eu atoms (space group: C2/m, a = 8.151(1) Å, b = 14.181(2) Å, c = 8.145(1) Å, β = 109.577(2)°). The structure models the [Al 4 ] as dual tetrahedra with the Al atom sites 37.5% occupied along with Eu present on the central site at 8% occupancy and the remainder of the site being vacant. The presence of the [Al 4 ] cluster is further supported by HRTEM. Electronic structure calculations show that this material is a semimetal with observed band crossings close to the Fermi level. Strong Al–Sb antibonding interactions were found from COHP calculations close to the Fermi level and provide the rationale for the deficiency of the Al cluster. Mössbauer spectroscopy on Eu-151 and Sb-121 provides oxidation states of 2+ and 3– along with the local environment. Magnetic susceptibility measurements can be described well with a Curie–Weiss law where an effective moment of 7.80 μB/mol Eu is obtained, consistent with Eu 2+ , and show canted antiferromagnetic behavior below 10 K. Temperature dependent resistivity shows a Kondo-like low-temperature upturn caused by enhanced scattering of the itinerant electrons with the 4f orbitals of Eu.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A Possible Radiation-Induced Transition from Monazite-(Ce) to Xenotime-(Y)

This study examines two pegmatitic monazite samples (2a and 4b, these numbers are related to a previous study) to determine their crystal chemistry and effects of internal radiation damage using synchrotron high-resolution powder X-ray diffraction and electron-probe micro-analysis. Both the huttonite and cheralite substitutions are discussed. Rietveld structure refinement of sample 2a shows three different phases [2a = monazite-(Ce), 2b = monazite-(Ce), and 2c = xenotime-(Y)] with distinct structural parameters. The changes among the unit-cell parameters between the two monazite-(Ce) phases is more pronounced in the a followed by the b and c unit-cell parameters. Sample 4a is a single-phase monazite-(Sm) that contains 0.164 apfu Th. Phase 2c with space group I41/amd arises from redistribution of La, Ce, Pr, Nd, Sm, Gd, Dy, Si, and Y atoms from those in monazite (space group P21/n). A possible cause for the phase transition from monazite-(Ce) to xenotime-(Y) is α-radiation events over a long geological time. However, other chemical processes cannot be ruled out as a cause for the transition.

structural variations↗
DOE OSTI2021

From Three-Dimensional Clathrates to Two-Dimensional Zintl Phases AMSb 2 (A = Rb, Cs; M = Ga, In) Composed of Pentagonal M–Sb Rings

Three new antimonide Zintl phases, RbGaSb 2 , CsGaSb 2 , and CsInSb 2 , were discovered during exploration of corresponding A–M–Sb (A = Rb, Cs; M = Ga, In) ternary systems while searching for new clathrates. The AGaSb 2 phases crystallize in the tetragonal space group P4 2 /nmc (No. 137) in the LiBS 2 structure type, while CsInSb 2 crystallizes in lower symmetry in the orthorhombic space group Cmce (No. 64) in the KGaSb 2 structure type with additional disorder of one of the Cs sites. The crystal structures of all three reported AMSb 2 compounds are composed of two-dimensional [MSb 2 ] – tetrahedral layers separated by Rb + or Cs + cations. [MSb 2 ] – layers are built from fused M–Sb pentagons and hexagons, which are also the main structural units for A 8 M 27 Sb 19 clathrate cages. The semiconductor nature of AMSb 2 was suggested by band structure calculations and confirmed by transport property characterization. CsGaSb 2 is a rare example of an n-type pnictide Zintl phase. Finally, all reported compounds exhibit low thermal conductivity typical for complex antimonides of heavy elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Creating superconductivity in WB 2 through pressure-induced metastable planar defects

High-pressure electrical resistivity measurements reveal that the mechanical deformation of ultra-hard WB 2 during compression induces superconductivity above 50 GPa with a maximum superconducting critical temperature, T c of 17 K at 91 GPa. Upon further compression up to 187 GPa, the T c gradually decreases. Theoretical calculations show that electron-phonon mediated superconductivity originates from the formation of metastable stacking faults and twin boundaries that exhibit a local structure resembling MgB 2 (hP3, space group 191, prototype AlB 2 ). Synchrotron x-ray diffraction measurements up to 145 GPa show that the ambient pressure hP12 structure (space group 194, prototype WB 2 ) continues to persist to this pressure, consistent with the formation of the planar defects above 50 GPa. The abrupt appearance of superconductivity under pressure does not coincide with a structural transition but instead with the formation and percolation of mechanically-induced stacking faults and twin boundaries. The results identify an alternate route for designing superconducting materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

The curious case of the structural phase transition in SnSe insights from neutron total scattering

Abstract At elevated temperatures SnSe is reported to undergo a structural transition from the low symmetry orthorhombic GeS-type to a higher symmetry orthorhombic TlI-type. Although increasing symmetry should likewise increase lattice thermal conductivity, many experiments on single crystals and polycrystalline materials indicate that this is not the case. Here we present temperature dependent analysis of time-of-flight (TOF) neutron total scattering data in combination with theoretical modeling to probe the local to long-range evolution of the structure. We report that while SnSe is well characterized on average within the high symmetry space group above the transition, over length scales of a few unit cells SnSe remains better characterized in the low symmetry GeS-type space group. Our finding from robust modeling provides further insight into the curious case of a dynamic order-disorder phase transition in SnSe, a model consistent with the soft-phonon picture of the high thermoelectric power above the phase transition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

The Zintl pnictides Yb10CdSb9 and Yb14CdSb11: New candidate thermoelectric materials

The synthesis of new materials is the lifeline of solid-state science, and it continues to offer us unique opportunities for testing various theoretical formulations and models on a practical material. Such an avenue, therefore, provides a breeding ground for technological innovations and advancements that can completely revolutionize our world. Here, we report the results of our exploratory syntheses in the Yb–Cd–Sb compositional space that lead to the identification of two new Zintl antimonides, namely, Yb10CdSb9 and Yb14CdSb11. Their crystal structures were established via single-crystal X-ray diffraction methods; the basic electronic and transport properties of the new materials were also characterized. Yb10CdSb9 crystallizes in a disordered variant of the tetragonal Ca10LiMgSb9 structure type with unit cell parameters a = 11.8473(8) Å and c = 17.1302(12) Å (space group P42/mnm). Yb14CdSb11 crystallizes in the tetragonal Ca14AlSb11 structure type with unit cell parameters: a = 16.605(3) Å and c = 12.144(7) Å (space group I41/acd). Although the structures of both compounds can be rationalized within the framework of the Zintl formalism, based on the partitioning of the valence electrons in the much disordered Yb10CdSb9 phase, the charge is indicative of a slightly electron-rich composition. Electronic structure calculations in both cases support the notion of intrinsic semiconductor behavior, as expected for a Zintl phase. The temperature dependence of the electrical resistivity of a single crystal of Yb10CdSb9 is in line with that, and the evolution of the Seebeck coefficient indicates an electron-dominated transport mechanism, and a respectable power factor of 0.71 μW/cm K2 at 460 K can be calculated for Yb10CdSb9. The electrical resistivity of Yb14CdSb11, however, evolves in a semimetallic manner, which could suggest an overdoped sample or degenerate semiconducting behavior.

Ogunbunmi, Michael O. (ORCID:0000000253409198)↗
DOE OSTI2021

Revealing pressure-driven structural transitions in the hybrid improper ferroelectric Sr 3 Sn 2 O 7

In this work, we combine diamond anvil cell techniques and synchrotron-based infrared spectroscopy with a detailed symmetry analysis and lattice dynamics calculations to uncover a series of pressure induced structural phase transitions in the hybrid improper ferroelectric Sr 3 Sn 2 O 7 . The microscopic character of each high pressure phase is determined by comparing the measured spectrum with the predicted vibrational patterns of several related but distinct candidate space groups. Our analysis reveals a sequence of compression-induced transitions from A2 1 am ↔ Pnab ↔ Acaa ↔ I4/mmm at room temperature. Remarkably, this space group progression matches the sequence of temperature-dependent structural transitions observed in Sr 3 Sn 2 O 7 between 77 and 1000 K. Other hybrid improper ferroelectrics display a similar set of transitions, suggesting that pressure and probably strain will be very effective tuning parameters for this entire class of materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Synthesis and Crystal Structures of Alkali (Na, Rb, Cs) Iron Phosphate Crystals

Three alkali-containing diphosphate crystals of A FeP 2 O 7 (A = Na, Rb, Cs) were synthesized through melt-crystallization. The crystal structures were determined using single-crystal X-ray diffraction (XRD) data. The synthesized diphosphates crystallized within the P 2 1 /c space group, and the structural parameters were compared to literature data of other A FeP 2 O 7 crystals within the P 2 1 /c space group.

36 MATERIALS SCIENCE↗
NASA NTRS1974

The two-dimensional tunnel structures of K3Sb5O14 and K2Sb4O11

The structures of K3Sb5O14 and K2Sb4O11 have been solved by the single-crystal X-ray direct method and the heavy-atom method, respectively. The structure of K3Sb5O14 is orthorhombic, with space group Pbam and cell parameters a = 24.247 (4), b = 7.157 (2), c = 7.334 (2) A, Z = 4. The structure of K2Sb4O11 is monoclinic, with space group C2/m and cell parameters a = 19.473 (4), b = 7.542 (1), c = 7.198 (1) A, beta = 94.82 (2) deg, Z = 4. A full-matrix least-squares refinement gave R = 0.072 and R = 0.067, respectively. In both structures, oxygen atoms form an octahedron around each Sb atom and an irregular polyhedron around each K atom. By sharing corners and edges, the octahedra form a skeleton network having intersecting b-axis and c-axis tunnels. The K(+) ions, which have more than ten oxygen near neighbors, are located in these tunnels. Evidence for K(+)-ion transport within and between tunnels comes from ion exchange of the alkali ions in molten salts and anisotropic temperature factors that are anomalously large in the direction of the tunnels.

Hong, H. Y.-P.↗
DOE OSTI2021

A Noncentrosymmetric Polymorph of LuRuGe

In this work, we report a new polymorph of LuRuGe, obtained in indium flux. This phase exhibits the noncentrosymmetric ZrNiAl-type structure with the space group $Ρ\bar 62m$ as determined by single-crystal X-ray diffraction. This polymorph can convert into another centrosymmetric polymorph (TiNiSi-type structure, space group Pnma ) at high temperatures. In this work, we performed electrical transport, magnetization, and specific heat measurements on this new phase. It shows metallic behavior with a Hall sign change from negative at 2 K to positive at 125 K. LuRuGe exhibits Pauli paramagnetism as the ground state with no local magnetic moments from either the Ru or Lu site. The Debye temperature Θ = 348 K and electronic coefficient γ e = 3.6 mJ K –2 mol –1 are extracted from the low-temperature specific heat data in LuRuGe. We also carried out first-principles density functional theory calculations to map out the electronic band structure and density of states. There are several electronic bands crossing the Fermi level, supporting a multiband scenario consistent with the Hall sign change. The density of states around the Fermi level is mainly from Ru 4d and Ge 4p electrons, indicating a strong hybridization between those atomic orbitals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Rare Earth Nitrate Hybrid Double Perovskites [Me 4 N] 2 [MLn(NO 3 ) 6 ] (M = Na–Cs; Ln = La–Gd, ex. Pm)

An exploration of the synthetic and structural phase space of rare earth hybrid double perovskites A 2 B'BX 6 (A = organocation, B' = M + , B = M 3+ , X = molecular bridging anion) that include X = NO 3 – and B' = alkali metal is reported, complementing earlier studies of the [Me 4 N] 2 [KB(NO 3 ) 6 ] (B = Am, Cm, La–Nd, Sm–Lu, Y) (Me 4 N = (CH 3 ) 4 N + ) compounds. In the present efforts, the synthetic phase space of these systems is explored by varying the identity of the alkali metal ion at the B'-site. Herein, we report three new series of the form [Me 4 N] 2 [B'B(NO 3 ) 6 ] (B = La–Nd, Sm–Gd; B' = Na, Rb, Cs). The early members of the Na-series crystallize in the trigonal space group R3̅ from La to Nd where a phase transition occurs in the phase between 273 and 300 K, going from R3̅ to the high-symmetry, cubic space group Fm3̅m. The preceding trigonal members of the Na-series also undergo phase transitions to cubic symmetry at temperatures above 300 K, establishing a decreasing trend in the phase-transition temperature. The remainder of the Na-series, as well as the Rb- and Cs-series, all crystallize in Fm3̅m at 300 K. The temperature-dependent phase behavior of the synthesized phases is studied via variable-temperature spectroscopic methods and high-resolution powder X-ray diffractometry. All phases were characterized via single-crystal and powder X-ray diffraction and Fourier transform infrared (FT-IR) and Raman spectroscopic methods. These results demonstrate the versatility of the perovskite structure type to include rare earth ions, nitrate ions, and a suite of alkali metal ions and serve as a foundation for the design of functional rare earth hybrid double perovskite materials such as those possessing useful multiferroic, optical, and magnetic properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Luminescent hybrid halides with various centering metal cations (Zn, Cd and Pb) and diverse structures

Organic–inorganic hybrid metal halides have been extensively studied because of their great potential in optoelectronics. Herein, we report three hybrid metal halides (Bmpip) 2 ZnBr 4 , (Bmpip) 2 CdBr 4 , and (Bmpip) 8 Pb 11 Br 30 (where Bmpip + is 1-butyl-1-methyl-piperidinium, C 10 H 22 N + ). (Bmpip) 2 ZnBr 4 and (Bmpip) 2 CdBr 4 crystallize in the P2 1 /c space group with zero-dimensional crystal structures with [MBr 4 ] 2− (M = Zn, Cd) tetrahedra isolated by Bmpip + . (Bmpip) 8 Pb 11 Br 30 crystallizes in the triclinic space group P$\overline{1}$ with combining macron] with one-dimensional corrugated chains constructed from face-sharing [PbBr 6 ] 4− octahedra. Furthermore, all of the compounds exhibit excellent ambient and thermal stability. Under UV excitation, all three compounds exhibit very broad emissions. Temperature-dependent photoluminescence measurements indicate that the broad emissions of (Bmpip) 2 ZnBr 4 and (Bmpip) 2 CdBr 4 can be attributed to both the organic cations and self-trapped excitons (STEs) and that the emission of (Bmpip) 8 Pb 11 Br 30 is assigned to STEs. Density functional theory calculations reveal that the three compounds adopt a direct band gap. This work enriches our understanding of the structure types of hybrid metal halides while revealing their diverse emission mechanisms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRSDate not supplied

X-Ray Diffraction Based Phase Identification in NiTiHf Shape Memory Alloys with Variable Hf Content

NiTiHf type shape memory alloys have been studied for use in high temperature actuator applications, the most studied of which is the NiTi-20Hf atomic % composition. In this study, six samples of NiTi-Hf including 20Hf, 30Hf, 35Hf, 40Hf, 45Hf, and 50Hf were evaluated by both 1D and 2D X-ray diffraction (XRD) to elucidate what phases and crystal structures were present at room temperature. Given small sample sizes and relatively large grains, multiple cross-sections were measured to increase the sampling statistics, and 2D XRD frames were collected to corroborate the 1D XRD data. Rietveld and structureless refinements were both performed, allowing for adjustments in orientation lattice constant, and structure factor. At room temperature, the primary martensitic phase in the NiTiHf alloys with 20 at% and lower Hf is a monoclinic B19’ phase (P1121/m space group). This phase was identifiable, even in small amounts, in the higher Hf samples. The primary phase in the 30 -50 at% Hf samples is an orthorhombic B33 (Cmcm space group) phase. This work supported thermal analyses indicating the phase transition paths from the two different room temperature martensitic phases to the B2 austenitic phase.

Laura Wilson↗